1. Technical Field
This description pertains generally to serial communications and particularly to providing a serial communications interface between a controller and a selected communications port.
2. Brief Description of Related Art
Semiconductor manufacturing test and other operations such as trace, debug, and emulation often use the interface signals defined in IEEE Standard 1149.1, commonly known as JTAG. This interface defines four to five leads used to send and receive serial data to and from a target circuit. This interface is broadly used in the industry today and has been extended beyond its original purpose of boundary scan.
The number of pins available for such serial communication to and from a target circuit is being reduced because of package size reductions that require most of the pins to be used for functional purposes.
Thus a need has arisen for a reduced pin interface to and from a target circuit. While such an interface can be used in semiconductor manufacturing test and other operations such as trace, debug and emulation, such an interface could also be used generally for other types of serial communication.